Let x be the number of students and y be the number of others. x + y = 300 (1) 2x + 3y = 670 (2) To solve the system, multiply eq(1) by 2 (both sides). Keep eq(2) as is. 2x + 2y = 600 (1') 2x + 3y = 670 (2') Subtract eq(1') from eq(2') (both sides). You will get 3y - 2y = 670-600 y = 70. Then from eq(1), x = 300-70 = 230. Answer. 230 students tickets were sold.